The defender spent two season on loan with Borussia Monchengladbach from 2015 onwards – but returned to Stamford Bridge this summer.
And, right from the start of the season, the Danish international has been given his chance by Antonio Conte – playing in the centre of Chelsea’s back three in the impressive win over Spurs at Wembley last week.
Having excelled during his time in Germany, winning Gladbach’s Player of the Year award after his first campaign with the club, the defender has spoken about the lessons he has learned and how they will help him to become a better player for Chelsea.
He told Chelsea’s official club programme for the Everton match: “I’ve heard people from the outside say that I went out on loan as a kid and I’ve returned as a first-team player, and I think that was the main objective.
“I’ve come back a little bit stronger in everything, both in terms of personality and the way I play.
“I think I’m a little bit cleverer because I always think about what could happen next on the pitch, what could go wrong. I’ve come back a bit wiser and more experienced.
“I didn’t want to only go out on one loan at one club, and then to another club, and then another. I wanted to be able to stabilise myself in one place and then come back ready.
“I’ve played two seasons in the Champions League and I’ve played against the greatest strikers in the game. Of course, that gives you much more confidence.
“You leave as a kid and you come back knowing you can play with the big names.
“Each day [in Chelsea training] it becomes more and more natural.
“It’s a little bit different, a little bit more disciplined than I’m used to, so I have to get used to that, and I’m starting to get there now. But right now I have to learn everything I can, as quickly as possible, and be ready to help my teammates.”